Clowns were comedic entertainers, usually found at circuses, known for wearing colourful clothes and bright face make-up. Many people regarded clowns as frightening rather than funny, sometimes to the point of having coulrophobia.
In the 19th century, clowns were members of the Night Travellers. (TV: From Out of the Rain)
Circa 1921, the First Doctor encountered a young Bing Crosby, who was working as a clown in Hollywood. (TV: The Daleks' Master Plan)
In the 1970s, the newly-regenerated Fourth Doctor briefly dressed in a harlequin clown costume. (TV: Robot)
In 2009, Sarah Jane Smith overcame her coulrophobia to battle a malevolent entity that sometimes masqueraded as Odd Bob the Clown. (TV: The Day of the Clown)
On Halloween of that year, the Hervoken compelled Jim Tozier to dress as an evil clown and attack Martha Jones. (PROSE: Forever Autumn)
The Eleventh Doctor found George's fear of clowns "understandable." (TV: Night Terrors)
Near the mid-21st century, advances in robot technology thanks to Alistair Gryffen and his Thought Matrix meant that Robot Clowns started appearing in circuses. Chuckles and Boris were two of these robot clowns. (TV: Robot Gladiators)
In 2050, a dream induced by the Bodach exploited Darius Pike's coulrophobia and he dreamed he was locked in Mariah with clowns. (TV: Dream-Eaters)
Joey the Clown and Clara the Clown were two clowns who served as the Celestial Toymaker's deadly pawns. (TV: The Celestial Toymaker)
The Second Doctor displayed clownish mannerisms, as noted disapprovingly by the First Doctor. (TV: The Three Doctors)
Ironically, the Third Doctor would later be forced to dress up like a clown. (AUDIO: The Paradise of Death)
Most of the clowns at the Psychic Circus were robots. (TV: The Greatest Show in the Galaxy)
When Chancellor Goth toyed with the Fourth Doctor in the Matrix, one of the forms he took was that of a clown which laughed at the Doctor in a reflection. (TV: The Deadly Assassin)
While in the Seventh Doctor's mind, Ace briefly encountered sinister clowns in a library. (PROSE: Timewyrm: Revelation)
On the planet Jenggel, one of the mercenaries there was named Clown and dressed himself in full clown makeup. (PROSE: Combat Rock)
A cartoon clown with blue hair was the mascot of the Gobocorp Freight Company. Centuries after the GFC ship Herald of Nanking crashed on the Gyre, the descendants of the survivors had taken to worshiping the clown mascot as the god Gobo. (PROSE: Night of the Humans)
One person's fear of clowns manifested itself in a room on the Minotaur's prison ship. The room stayed behind after the person's death. Lucy Hayward, Rita and Amy Pond all encountered it, but were unimpressed. (TV: The God Complex)